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The cyst wall of some ciliated protists is composed of four layers, ectocyst, mesocyst, endocyst, and the granular layer. The ectocyst is the outer layer and contains a plug-like structure through which the vegetative cell reemerges during excystation. Interior to the ectocyst, the thick mesocyst is compact yet stratified in density.
Entamoeba coli is a non-pathogenic species of Entamoeba that frequently exists as a commensal parasite in the human gastrointestinal tract. E. coli (not to be confused with the bacterium Escherichia coli) is important in medicine because it can be confused during microscopic examination of stained stool specimens with the pathogenic Entamoeba histolytica. [1]
A trophozoite (G. trope, nourishment + zoon, animal) is the activated, feeding stage in the life cycle of certain protozoa such as malaria-causing Plasmodium falciparum and those of the Giardia group. [1]
Once in the intestine of its host, cysts undergo excystation into the trophozoite stage that feeds on intestinal bacteria. [3] Each cyst gives rise to only one trophozoite. [9] Retortamonas trophozoites then multiply asexually through lateral binary fission. [2] [9] Eventually the trophozoites encyst, and the cysts are discharged via feces.
Life-cycle of Entamoeba histolytica. Entamoeba histolytica is an anaerobic parasitic amoebozoan, part of the genus Entamoeba. [1] Predominantly infecting humans and other primates causing amoebiasis, E. histolytica is estimated to infect about 35-50 million people worldwide. [1]
These cysts on reaching the terminal ileum region of the gastrointestinal tract give rise to a mass of proliferating cells, the trophozoite form of the parasite, by the process of excystation. [22] Symptoms of this infection include diarrhea with blood and mucus, and can alternate between constipation and remission, abdominal pain, and fever.
Phoronts go through metamorphosis to prepare for excystation. Metamorphosis changes the body shape, organization, and physiology of the phoront to allow for rapid ingestion and storage of large amounts of food. Histotrophic phoronts metamorphose within a few hours of encysting on their hosts.
Once ingested, the cyst travels through the digestive system unaffected until it reaches the small intestine, where it encounters several triggers, that have been found to induce excystation. Such triggers include, low glucose, [10] osmotic shock, [1] and a combination of water, bicarbonate, and bile. [11]